<!DOCTYPE html>
<html lang="en">
  <head>
    <meta charset="UTF-8" />
    <meta name="viewport" content="width=device-width, initial-scale=1.0" />
  </head>
  <body>
    <style>
      /*  11*/
      h1.y {
        color: red;
      }
      /* 1 */
      h1 {
        color: green !important;
      }
      /* 10 */
      .group {
        color: indigo;
        font-size: 33px;
      }
      #app {
        color: olive;
      }
    </style>
    <h1 class="y group" id="app" style="color: orangered">yahoo</h1>
    <h2 class="y">chrome</h2>
    <h1 class="t">tom</h1>

    <style>
      h2 {
        color: black;
      }
      h2.hd {
        color: red;
      }
      div.main h2 {
        color: blue;
      }
      div.main h2 {
        color: yellow;
      }
    </style>
    <div class="main">
      <h2>houdunren</h2>
    </div>
  </body>
</html>
